วารสารวชิาการ คณะเทคโนโลยอุีตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา... ๒๕๕๐ 43

CCCCTA Based-Dual-Mode Universal Biquad Filterอาจารยวิ์นยั ใจกลา้*

* อาจารย์ประจำสาขาวิชาเทคโนโลยีอิเล็กทรอนิกส์ คณะเทคโนโลยีอุตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา

Abstract- This article presents a dual-mode (voltage-mode and current-mode)universal biquadratic filter performing completely standard functions: low-pass, high-pass,band-pass, band-reject and all-pass functions, based on current controlled current conveyortransconductance amplifier (CCCCTA). The features of the circuit are that: the quality factorand natural frequency can be tuned electronically via the input bias currents: the circuitdescription is very simple, consisting of merely single CCCCTA and 2 capacitors: the circuitcan provide either the voltage-mode or current-mode filter without changing circuit topology.Additionally, each function response can be selected by suitably selecting input signals withdigital method. Without any external resistors, the proposed circuit is very suitable to furtherdevelop into an integrated circuit. The PSPICE simulation results are depicted. The givenresults agree well with the theoretical anticipation. The maximum power consumption isapproximately 1.81mW at ±±±±±1.5V supply voltages.

Index Terms- Biquad filter, Dual-mode, CCCCTA

I. INTRODUCTIONAn analog filter is an important block and

widely used for continuous-time signal processing.It can be found in many fields: for instance,communication, measurement and instrumentationand control systems [1-2]. One of most popularanalog filters is a universal biquadratic filter sinceit can provide several functions. Nowadays, auniversal filter working in current-mode has beingbeen more popular than voltage-mode one. Sincethe last decade, there has been much effort toreduce the supply voltage of analog systems. Thisis due to the command for portable and battery-powered equipment. Since a low-voltage operatingcircuit becomes necessary, the current-modetechnique is ideally suited for this purpose. Actually,

a circuit using the current-mode technique hasmany other advantages: for example, larger dynamicrange, higher bandwidth, greater linearity, simplercircuitry and lower power consumption [3-4].However, in present, the voltage-mode circuits arestill used in some applications.

The current conveyor transconductandamplifier (CCTA) is a reported active component,especially suitable for a class of analog signalprocessing [5]. The fact that the device can operatein both current and voltage-modes providesflexibility and enables a variety of circuit designs.In addition, it can offer advantageous features suchas high-slew rate, higher speed, wide bandwidthand simple implementation [5]. However, the CCTAcan not control the parasitic resistance at X (Rx)

วารสารวชิาการ คณะเทคโนโลยอุีตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา... ๒๕๕๐44

port so when it is used in some circuits, it mustunavoidably require some external passivecomponents, especially the resistors. This makesit not appropriate for IC implementation due tooccupying more chip area, high power consumptionand without electronic controllability. On the otherhand, the introduced current-controlled currentconveyor transconductand amplifier (CCCCTA)[6-7] has the advantage of electronic adjustabilityover the CCTA.

In many applications, voltage and current-mode circuits are used to be connected whichcauses some difficulties that can be overcame byusing voltage-to-current and current-to-voltageconverters at the interface of these circuits. DuringV-I interfacing, it is also possible to perform signalprocessing at the same time so that the totaleffectiveness of the electronic circuitry can beincreased [8]. The literature surveys show that thedual-mode universal filter circuits using differenthigh-performance active building blocks such asOTAs [9-11], current feedback op-amps (CFOAs)[12-14], Four-Terminal Floating Nullors (FTFNs)[15-17] and current conveyors [18-22], have beenreported. Unfortunately, these reported circuits sufferfrom one or more of following weaknesses:

Excessive use of the active and/or passiveelements [8, 12-15, 17-22].Require changing circuit topologies to achieveseveral functions [9-10, 13-15].Lack of electronic adjustability [8, 12-15,17-21].Can not provide completely standard functions[8-9, 11, 13-14, 17-18, 20].Can not provide functions both in voltage andcurrent-modes with the same topology [11,13, 15, 17].

This work is arranged to propose a newvoltage/current-mode universal biquadratic filter,emphasizing on use of single CCCCTA. The featuresof proposed circuit are that: the proposed universalfilter can provide completely standard functionsboth in voltage-mode and current-mode withoutchanging circuit topology by appropriately selectingthe input signals: the circuit description is verysimple, it consists of 1 CCCCTA and 2 capacitors,which is suitable for fabricating in monolithic chip:the filter does not require any external resistor. Inaddition, the natural frequency and the bandwidthcan be tuned electronically by adjusting the biascurrents. Its performances are illustrated by PSPICEsimulations, they show good agreement asmentioned.

II. CIRCUIT PRINCIPLEA. Basic Concept of CCCCTA

The CCCCTA properties are similar to theconventional CCTA, except that the CCCCTA hasfinite input resistance Rx at the x input terminal.This parasitic resistance can be controlled by thebias current IB1 as shown in the following equation

(1)

where (2)

gm is the transconductance of the CCCCTA andVT is the thermal voltage. The symbol and theequivalent circuit of the CCCCTA are illustrated inFig. 1(a) and (b), respectively.

(a) (b)Figure 1. CCCCTA (a) Symbol (b) Equivalent circuit.

วารสารวชิาการ คณะเทคโนโลยอุีตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา... ๒๕๕๐ 45

B. Proposed Dual-Mode Universal Biquad FilterThe proposed dual-mode universal filter

is shown in Fig. 2, where IB1 and IB2 are inputbias currents of CCCCTA. They are used to controlthe corresponding parasitic resistance andtransconductance.

For voltage-mode case, where Iin1=Iin2=Iin3=0,straightforwardly analyzing the filter in Fig. 2, theoutput voltage can be obtained as

(3)

Figure 2. Proposed dual-mode universal filter

TABLE IThe Vin1, Vin2 and Vin3 values selection for

each filter function response

From Eq. (3), Vin1, Vin2 and Vin3 can bechosen as in Table I to obtain a standard functionof the 2nd-order network. From Table I, it shouldbe remarked that, in case of the BP, BR, AP andLP, the circuit condition: Rx=1/gm is required. For current-mode case, where Vin1=Vin2=Vin3=0,straightforwardly analyzing the circuit in Fig. 2,the output current can be obtained as

(4)

From Eq. (4), the magnitudes of inputcurrents Iin1, Iin2 and Iin3 can be chosen as in TableII to obtain a standard function of the network.The circuit of digital selection can be seenin [23].

TABLE IIThe Iin1, Iin2 and Iin3 values selection for

each filter function response

From Eqs. (3)-(4), for dual-mode, thenatural frequency (ω0) and quality factor (Q0) ofeach filter response can be expressed as

(5)

Substituting intrinsic resistance andtransconductance as depicted in Eq. (2), it yields

(6)

From Eqs. (5) and (6), by maintaining theratio IB1 and IB2 to be constant, it can be remarkedthat the natural frequency can be adjusted by IB1

and IB2 without affecting the quality factor. Inaddition, bandwidth (BW) of the system can beexpressed by

(7)

We found that the bandwidth can belinearly controlled by IB1. Moreover, it can be seenthat the natural frequency can be also adjustedorthogonally from the bandwidth by varyingIB2. Moreover, it is easy cascading both in

วารสารวชิาการ คณะเทคโนโลยอุีตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา... ๒๕๕๐46

current-mode and voltage-mode. In current-modeconfiguration it has high output impedance, involtage-mode the output impedance is quit low.

C. Circuit SensitivitiesThe sensitivities of the proposed circuit

can be found as

(8)

(9)

and (10)

Therefore, all the active and passivesensitivities are equal or less than unity inmagnitude.

D. Non-ideal caseFor non-ideal case, the and of CCCCTA

can be respectively characterized by

(11)

(12)

and (13)

α, γ and β are transferred error valuesdeviated from one. In the case of non-idea andreanalysis of proposed filter circuit in Fig. 2, itrespectively yields the output voltage and currentas

(14)

(15)

In this case, the ω0 and Q0 are changed to

(17)

while BW is still equal to Eq. (7). Actually, thesedeviations are very small and can be ignored.Practically, from Eqs. (11-13), α, γ and β originatefrom intrinsic resistances and stray capacitancesin the active elements. These errors affect thesensitivity to temperature and high frequencyresponse of the proposed circuit. From Eqs.(14) and (15), it is found that the current andvoltage gains depend on the temperature andfrequency variations, then the CCCCTA should becarefully designed to achieve these errors as lowas possible.

Figure 3. Internal construction of CCCCTA

III. SIMULATION RESULTSTo prove the performances of the

proposed circuit, the PSPICE simulation programwas used for the examinations. The PNP and NPNtransistors employed in the proposed circuit weresimulated by respectively using the parameters ofthe PR200N and NR200N bipolar transistors ofALA400 transistor array from AT&T [24]. Fig. 3depicts schematic description of the CCCCTA usedin the simulations. The circuit was biased with±1.5V supply voltages. C1=C2=1nF and IB1=54μA,

IB2=200μA are chosen. It yields the naturalfrequency of 540.75kHz, while calculated valueof this parameter from Eq. (7) is 612.45kHz. Theresults shown in Fig. 4 are the gain and phaseresponses of the proposed biquad filter in voltage-

วารสารวชิาการ คณะเทคโนโลยอุีตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา... ๒๕๕๐ 47

mode obtained from Fig. 2. There are seen thatthe proposed filter in voltage-mode can providelow-pass, high-pass, band-pass, band-reject andall-pass functions dependent on selection as shownin Table I, without modifying circuit topology.

Figure 4. Gain and phase responses of thebiquad filter in voltage-mode for

(a) LP (b) HP (c) BP (d) BR (e) AP.

The gain and phase responses of theproposed biquad filter in current-mode are shownin Fig. 5. There are seen that the proposed filter incurrent-mode can also provide completely standardfunctions dependent on selection as shown inTable II. Fig. 6 shows gain responses of band-pass function where IB1 and IB2 are equally set tokeep the ratio to be constant and changed forseveral values. It is found that pole frequency canbe adjusted without affecting the quality factor, asdepicted in Eq. (6). Maximum power consumptionis about 1.81mW.

Figure 5. Gain and phase responses of thebiquad filter in voltage-mode for

(a) LP (b) HP (c) BP (d) BR (e) AP.

วารสารวชิาการ คณะเทคโนโลยอุีตสาหกรรม มหาวิทยาลัยราชภัฏสวนสุนันทา... ๒๕๕๐48

Figure 6. Current-mode band-pass responses fordifferent values of IB1 and IB2

IV. CONCLUSIONThe dual-mode universal biquadratic filter

based on CCCCTA has been presented. Theadvantages of the proposed circuit are that: it

performs low-pass, high-pass, band-pass, band-reject and all-pass functions dependent on anappropriate selection of three signals in dual-mode:the quality factor and the natural frequency can beelectronically controlled via input bias currents, itis easily modified to use in control systems usinga microcontroller [3]. The circuit descriptioncomprises only 1 CCCCTA and 2 capacitors. Withmentioned features, it is very suitable to realizethe proposed circuit in monolithic chip to use inbattery-powered, portable electronic equipmentssuch as wireless communication system devices.

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